see mesomeric effect is what u have in the form of resonance or conjugation in a benzene ring with substitution for example consider chloro benzene it shows +M effect as it donates its lone pair to the ring

electromeric effect is a temporary one take for example an aldehyde ie C=0 group here on the approach of a electro or nucleophile it undergoes elctromerisation to give C+-O- to provide a site for attack!!!!

hyperconjugative resonance takes place between alpha hydrogen and the double bond or carbocation or free radical it is also known as no bond resonance do u want further explaination???Rate me if useful!!!